This invention relates generally to methods and apparatus for attaching soft tissue to bone, and more particularly to anchors and methods for securing connective tissue, such as ligaments or tendons, to bone. The invention has particular application to arthroscopic surgical techniques for reattaching the rotator cuff to the humeral head, in order to repair the rotator cuff.
It is an increasingly common problem for tendons and other soft, connective tissues to tear or to detach from associated bone. One such type of tear or detachment is a xe2x80x9crotator cuffxe2x80x9d tear, wherein the supraspinatus tendon separates from the humerus, causing pain and loss of ability to elevate and externally rotate the arm. Complete separation can occur if the shoulder is subjected to gross trauma, but typically, the tear begins as a small lesion, especially in older patients.
To repair a torn rotator cuff, the typical course today is to do so surgically, through a large incision. This approach is presently taken in almost 99% of rotator cuff repair cases. There are two types of open surgical approaches for repair of the rotator cuff, one known as the xe2x80x9cclassic openxe2x80x9d and the other as the xe2x80x9cmini-openxe2x80x9d. The classic open approach requires a large incision and complete detachment of the deltoid muscle from the acromion to facilitate exposure. The cuff is debrided to ensure suture attachment to viable tissue and to create a reasonable edge approximation. In addition, the humeral head is abraded or notched at the proposed soft tissue to bone reattachment point, as healing is enhanced on a raw bone surface. A series of small diameter holes, referred to as xe2x80x9ctransosseous tunnelsxe2x80x9d, are xe2x80x9cpunchedxe2x80x9d through the bone laterally from the abraded or notched surface to a point on the outside surface of the greater tuberosity, commonly a distance of 2 to 3 cm. Finally, the cuff is sutured and secured to the bone by pulling the suture ends through the transosseous tunnels and tying them together using the bone between two successive tunnels as a bridge, after which the deltoid muscle must be surgically reattached to the acromion. Because of this maneuver, the deltoid requires postoperative protection, thus retarding rehabilitation and possibly resulting in residual weakness. Complete rehabilitation takes approximately 9 to 12 months.
The mini-open technique, which represents the current growing trend and the majority of all surgical repair procedures, differs from the classic approach by gaining access through a smaller incision and splitting rather than detaching the deltoid. Additionally, this procedure is typically performed in conjunction with arthroscopic acromial decompression. Once the deltoid is split, it is retracted to expose the rotator cuff tear. As before, the cuff is debrided, the humeral head is abraded, and the so-called xe2x80x9ctransosseous tunnelsxe2x80x9d, are xe2x80x9cpunchedxe2x80x9d through the bone or suture anchors are inserted. Following the suturing of the rotator cuff to the humeral head, the split deltoid is surgically repaired.
Although the above described surgical techniques are the current standard of care for rotator cuff repair, they are associated with a great deal of patient discomfort and a lengthy recovery time, ranging from at least four months to one year or more. It is the above described manipulation of the deltoid muscle together with the large skin incision that causes the majority of patient discomfort and an increased recovery time.
Less invasive arthroscopic techniques are beginning to be developed in an effort to address the shortcomings of open surgical repair. Working through small trocar portals that minimize disruption of the deltoid muscle, a few surgeons have been able to reattach the rotator cuff using various bone anchor and suture configurations. The rotator cuff is sutured intracorporeally and an anchor is driven into bone at a location appropriate for repair. Rather than thread the suture through transosseous tunnels which are difficult or impossible to create arthroscopically using current techniques, the repair is completed by tying the cuff down against bone using the anchor and suture. Early results of less invasive techniques are encouraging, with a substantial reduction in both patient recovery time and discomfort. The major stumbling block for many surgeons is the extreme difficulty in performing the procedure with the currently available tools and techniques.
There are various bone anchor designs available for use by an orthopedic surgeon for attachment of soft tissues to bone. The basic commonality between the designs is that they create an attachment point in the bone for a suture that may then be passed through the soft tissues and tied, thereby immobilizing the soft tissue. This attachment point may be accomplished by different means. Screws are known for creating such attachments, but suffer from a number of disadvantages, including their tendency to loosen over time, requiring a second procedure to later remove them, and their requirement for a relatively flat attachment geometry.
Another approach is to utilize the difference in density in the cortical bone (the tough, dense outer layer of bone) and the cancellous bone (the less dense, airy and somewhat vascular interior of the bone). There is a clear demarcation between the cortical bone and cancellous bone, where the cortical bone presents a kind of hard shell over the less dense cancellous bone. In one prior art approach that utilizes this physiological construct, the anchor is designed so that it has a longer axis and a shorter axis and is usually pre-threaded with suture. These designs use a hole in the cortical bone through which an anchor is inserted. The hole is drilled such that the shorter axis of the anchor will fit through the diameter of the hole, with the longer axis of the anchor being parallel to the axis of the drilled hole. After deployment in to the cancellous bone, the anchor is rotated 90xc2x0 so that the long axis is aligned perpendicularly to the axis of the hole. The suture is pulled, and the anchor is seated up against the inside surface of the cortical layer of bone. Due to the mismatch in the dimensions of the long axis of the anchor and the hole diameter, the anchor cannot be retracted proximally from the hole, thus providing resistance to pull-out.
Examples of such an approach are seen in U.S. Pat. No. 5,879,372 to Bartlett and U.S. Pat. No. 6,007,4567 to Bonutti. Depending upon the density of the cancellous bone, these devices may be somewhat difficult to deploy. If the cancellous bone density is high, it is difficult to force the inserted anchor to rotated into a secured position.
It is possible to utilize other anchor geometry to take advantage of the cortical and cancellous bone interface. Various methods of creating an expanded or tortuous frontal area beneath the cortical surface have been described in the prior art. An example of this approach is seen is U.S. Pat. No. 5,797,963 to McDevitt. This patent describes a sub-cortical anchor that utilizes a tapered flaring tool which deploys fingers circumferentially disposed about the periphery of the anchor to engage the cancellous bone and to resist retraction through the limited diameter hole in the cortical bone. A similar approach is disclosed in U.S. Pat. Nos. 5,690,649 and 6,022,373, both to Li. The Li patents describe an anchor that incorporates two cylindrical halves with fingers that are interdigitated. When a force is imposed on the two halves, the interlocked fingers cause the deflection and deployment of the concomitant adjacent fingers on the opposite half, creating the expanded areas that resists pullout. In all of these designs, the expanding mechanism is adapted to resist axial loading, but there is no disclosure that they are capable of rotational fixation.
Still other prior art approaches have attempted to us a xe2x80x9cpop rivetxe2x80x9d approach. This type of design requires a hole in the cortical bone into which a split shaft is inserted. The split shaft is hollow, and has a tapered plug leading into its inner lumen. The tapered plug is extended out through the top of the shaft, and when the plug is retracted into the inner lumen, the tapered portion causes the split shaft to be flared outwardly, ostensibly locking the device into the bone.
Other methods of securing soft tissue to bone are known in the prior art, but are not presently considered to be feasible for shoulder repair procedures, because of physicians"" reluctance to leave anything but a suture in the capsule area of the shoulder. The reason for this is that staples, tacks, and the like could possibly fall out and cause injury during movement. As a result of this constraint, the attachment point often must be located at a less than ideal position. Also, the tacks or staples require a substantial hole in the soft tissue, and make it difficult for the surgeon to precisely locate the soft tissue relative to the bone.
By now it should be clear that many existing fastener technologies have been adapted for use in creating an anchor point for sutures in bone. Screws, pop rivets, and the like are certainly adaptable to the wooden-like structure exhibited by bone. However, as previously discussed, bone also incorporates a structure that presents a hard, dense, outside surface and a softer, less dense core. Because of this structure, another type of fastener, commonly referred to as a xe2x80x9cmoly boltxe2x80x9d or xe2x80x9cexpandable boltxe2x80x9d, may be adapted for use in the bone. These types of fasteners were originally designed for creating attachment points in plaster board walls where the wall is analogous to the hard cortical bone surface and the airspace or insulation space is analogous to the softer cancellous bone.
One example of such a fastener is shown in U.S. Pat. No. 4,828,439, to Giannuzzi. A screw anchor is disclosed which includes a four-legged compressible shank whose normal shape is diamond-like, the front legs of the shank being joined together by a front apex hinge and the rear legs being joined to the front legs by side apex hinges. The rear legs terminate in feet whose adjacent soles normally assume the form of an inverted V-inlet. A socket whose bore lies in axial registration with a hole in the front apex of the shank is secured by a pair of normally outstretched resilient webs to the respective rear legs. To install the anchor, its side apex hinges are manually compressed to collapse the shank into a tongue which is then inserted through a hole drilled in the wall until the socket is seated therein and the shank which is now behind the wall resumes its diamond-like shape. Then a screw for holding the fixture against the wall is inserted in the socket bore and turned therein until its tip is intercepted by the inlet which is dilated thereby to admit the screw. As the turning screw continues to advance, its crests engage the soles of the feet to force the rear legs apart and in doing so compels the shank to assume a triangular shape. At the conclusion of the screw advance, its tip is threadedly received in the hole of the front apex to create behind the wall a triangular truss in which the screw forms a central strut. It is clear in reference to this patent that the principal fixation is axial, and that no provision for rotational fixation is provided.
U.S. Pat. No. 5,893,850 to Cachia describes a fixation device of a type useful for connecting two or more bone segments during the healing process. In the preferred embodiment, the device comprises an elongate pin having a distal anchor thereon. This distal anchor is essentially an umbrella-shaped end to the pin that may be selectively collapsed for pushing through a hole drilled through the bone segments, and then deployed at the distal end of the hole to prevent the elongate pin from retracting back through the hole. A proximal anchor is co-axially and slidably disposed with respect to the pin, and fixable to accommodate different bone dimensions and permit appropriate tensioning of the fixation device. An additional embodiment may be used when the preferred embodiment is not possible to deploy. This situation may occur, for example, when there is not a distal bone surface to allow for the deployment of the umbrella-shaped pin end. This embodiment describes a construction with multiple, axially expanding strips that are configured to engage the cancellous bone to resist axial withdrawal of the main body of the anchor. The patent describes two or more sets of strips, as the disclosed function of the anchor is to fixate at least two bone segments together to promote healing of the bone. There is no mention of providing an anchor point to which a suture may be secured, nor is one contemplated.
Still another bone fixation device of interest is disclosed in U.S. Pat. No. 5,501,695 to Anspach, Jr. et al. In this patent, there is disclosed a bone anchor apparatus which comprises a rivet body having a lower annular portion 12 and an upper annular portion 100. The lower annular portion includes an outer surface formed as an extension of the outer surface of the upper annular portion. Because the thickness of the lower annular portion is less than that of the upper annular portion, the upper annular portion acts as an annular step or stop. A plurality of longitudinal slots are formed on the outer surface of the lower annular portion, and lengthwise ribs are formed between the slots. The apparatus comprises multiple components, including, additionally, a separate puller, including a head and a puller rod, which extends upwardly through the inner diameter of the lower and upper parts of the rivet""s annular portions. In operation, the puller is actuated upwardly until it strikes the annular step, thereby axially compressing the lower annular portion so that the ribs are expanded radially outwardly.
There is shown in FIG. 8 of the ""695 patent a disk 38 which includes apertures 40 for accommodating attachment of a suture 42 thereto. This disk, however, remains above the surface of the bone once the anchor is in place. While the ""695 patent discloses an apparently functional device, it is complicated and difficult to use in the close quarters attendant to arthroscopic procedures.
It may be seen, then, that as different fasteners have been adapted for use in providing an anchor point for a surgical suture in conjunction with attaching soft tissues to bone, various problems and challenges have appeared. Although some of those problems and challenges have been addressed, not all of the requirements for simple, secure fixation have been met, particularly for creating a simple and facile apparatus and method for soft tissue fixation that may be deployed arthroscopically.
What is needed, therefore, is a new arthroscopic approach for providing an anchor point in bone structure, wherein the anchor resides completely below the superficial cortical bone surface, provides both axial and rotational fixation, is better for the patient, is uncomplicated to use, thereby saving time during the repair procedure, and is easily mastered by properly skilled personnel.
The present invention solves the problems outlined above by providing an innovative bone anchor and connective techniques which permit a suture attachment which lies entirely beneath the cortical bone surface. The anchor design permits easy and facile insertion into the bone, and simple and secure anchoring after deployment.
More particularly, there is provided by the inventive apparatus a means and method for attaching soft or connective tissue to bone, comprising a hollow cylinder having a longitudinal axis and a periphery which is adapted to be inserted into a hole pre-drilled into bone. The cylinder is adapted to have a plurality of slits and ribs running parallel to or roughly along the longitudinal axis of the cylinder and equally distributed about the diameter of the cylinder. For example, there may be 4 slits defining 4 ribs, equally spaced at 90xc2x0 intervals around the cylinder. These ribs are predisposed to bend in a direction radially outwardly from their resting position when an axial load is placed upon the cylinder. The ribs bend in a characteristic fashion that has each end of the ribs bending outwardly, with the center of the rib bending at an angle approximately twice that of the ends, and in the opposite direction. Such structure creates a xe2x80x9cflowerxe2x80x9d or an expansion of the outside diameter of the cylinder. The xe2x80x9cflowerxe2x80x9d moniker is chosen because, as the ribs bend outwardly away from the body of the cylinder, they create xe2x80x9cpetalsxe2x80x9d around the periphery of the cylinder.
As previously mentioned, the structure of the bone in the humerus, for example, has a dense outer layer called the cortical bone, and a lacy, cellular inner structure called the cancellous bone. When the hole for the present invention is drilled in the bone, the hole extends through the cortical layer and into the cancellous layer. As it may be seen, if the anchor is placed such that the deployment of the ribs creating the flower is undertaken below the cortical layer and in the cancellous layer, it is not possible to remove the anchor proximally from the hole, as it is trapped underneath the cortical layer. This provides an extremely secure anchoring point that distributes any load placed upon it over a relatively large surface area when compared to anchors known in the prior art. This distribution of load is a significant advance in the art, and allows loads that typically would surpass the tensile strength of the sutures used to secure the tissues. In other words, because of the innovative design of the anchor, the sutures will break before the anchor is displaced.
In the present state of the art, as discussed supra, the sutures which are passed through the tissues to be attached to bone typically are threaded through a small eyelet incorporated into the head of the anchor and then secured by tying knots in the sutures. Although the anchor means herein described certainly are amenable to such attachment, if desired, an eyelet is by no means the only way that sutures may be secured to the bone anchor. Other means of attachment which allow for adjustable, releasable suture fixation that does not require knot tying is contemplated.
It may be seen that the geometry created by the present invention may provide both axial and rotational means of fixation for the bone anchor. The petals of the flower, as previously discussed, do prevent the anchor from being pulled axially out through the hole through which it was deployed. Also, because of the fact that the petals expand radially outward from the body of the anchor, they create anchor points within the cancellous bone that also resist rotational forces.
Additionally, the inventors have refined the xe2x80x9cflowerxe2x80x9d concept to incorporate a unique and advantageous modification to the pattern of slits and ribs. By creating, in one preferred embodiment, the slits and ribs on a bias (in other words, at an acute angle when viewed relative to the axis of the body of the anchor), a different deployment mechanism is effected. With substantially axial ribs and slits, the ribs fold up in their characteristic fashion as previously described, i.e. each end of the ribs bending outwardly, with the center of the rib bending at an angle twice that of the ends and in the opposite direction and ultimately the two ends of the ribs flattening against each other. Instead, when the ribs are formed on the aforementioned bias, they tend to bend in a semi circular fashion and stack on top of each other, forming overlapping petals that create a substantial bulge in the body of the anchor.
More particularly, there is provided an apparatus for attaching connective tissue to bone, which comprises a body having a longitudinal axis, a proximal end, and a distal end, which is adapted to be inserted into a bone. The anchor body includes a plurality of spaced slits, preferably at least six, disposed about the periphery thereof, wherein each of the slits has a length, and a distance x between two adjacent slits at a first location along the length of each of the slits is smaller than a distance y between the two adjacent slits at a second location along the length of each of the slits. Preferably, the slits each comprise an end, wherein the first location is proximate to an end of each of the adjacent slits and the second location being in a middle region of each of the adjacent slits.
More preferably, each of the slits further comprises an angled surface at at least one, and preferably both ends thereof, wherein each of the angled surfaces, or xe2x80x9cnotchesxe2x80x9d, extends depthwise into a wall forming the body. In preferred embodiments, the anchor body is a generally cylindrical body having an outer circumferential wall defining an inner lumen.
In some embodiments of the invention, the plurality of spaced slits are generally parallel to the longitudinal axis. In other, presently preferred embodiments, the plurality of spaced slits each lie at an acute angle relative to the longitudinal axis. The acute angle is preferably between 0 and 45 degrees.
The anchoring apparatus should include a plurality of spaced slits that are sufficient in number such that when an axial length of the body is shortened, a plurality of ribs which are disposed between each of the plurality of slits are caused to each expand radially to form respective petals, each of the petals overlap adjacent ones thereof.
In another aspect of the invention, there is provided an apparatus for attaching connective tissue to bone, comprising a body having a longitudinal axis, a proximal end, and a distal end, which is adapted to be inserted into a bone. The anchoring body includes a plurality of spaced slits disposed about the periphery thereof, each of the slits having a length and an angled surface at an end thereof, extending depthwise into a wall forming the body. Preferably, each of the slits has an angled surface at each end thereof, extending depthwise into the body wall.
In preferred embodiments, a distance x between two adjacent slits at a first location along the length of each one of the adjacent slits is smaller than a distance y between the same two adjacent slits at a second location along the length of each one of the adjacent slits. Such a configuration has been found to substantially reduce the axial forces required to deploy the anchor, once inserted into desired bone structure. Preferably, the first location is proximate to an end of each of the slits and the second location is in a middle region of each of the adjacent slits.
In yet another aspect of the invention, there is disclosed a method of fabricating an apparatus for attaching connective tissue to bone, which comprises a step of making a pattern of a bone anchor using a bio-compatible material. A plurality of spaced slits are disposed across a width of the pattern, such that adjacent ones of the slits are closer together at a first location along a length thereof and being farther apart at a second location along the length. The pattern is then formed into an anchor body, which is preferably generally cylindrical. The first location is preferably near an end of each of the respective adjacent slits and the second location is in a middle region of each of the respective adjacent slits.
Preferably, the method includes an additional step of forming an angled surface extending depthwise into the pattern at an end of each of the spaced slits, and, more preferably, at each end of each of the spaced slits. In order to form the slits in the aforementioned manner, it is preferred that a cutting wheel be used to form the spaced slits.
In still another aspect of the invention, there is disclosed a method of fabricating an apparatus for attaching connective tissue to bone, which comprises steps of making a pattern of a bone anchor using a bio-compatible material, and forming a plurality of spaced slits across a width of the pattern, such that an end of each of the slits includes an angled surface extending depthwise into the pattern. The pattern is then fabricated into an anchor body.